1. Field of the Invention
This invention relates to the field of automotive transmissions. It pertains particularly to such transmissions providing synchronized speed ratio changes.
2. Description of the Prior Art
Conventional manually-operated automotive transmissions employ a system of meshing gear-pinion pairs supported on a main shaft and a parallel countershaft or layshaft. However, various attempts have been made to use epicyclic gearing in a manual transmission. Epicyclic gearing is a system of gears in which one or more gears travel around the inside or outside of another gear whose axis is fixed. An epicyclic train is a combination of epicyclic gears, in which some or all the gears rotate about an axis and translate or revolve around that axis.
U.S. Pat. No. 787,908 describes a manual transmission producing a direct drive forward speed ratio and forward and reverse low speed ratios by alternately engaging two brake bands and a clamping disc, each associated with one of these speed ratios. The transmission includes a cluster pinion having three gears, each pinion meshing with a gear driven by an engine shaft.
U.S. Pat. No. 1,005,186 describes a transmission that produces low speed forward drive and reverse drive by selective engaging brake bands for holding sun gears against rotation. A cluster gear having three planet pinions meshes with an output sun gear, a forward drive sun gear and a reverse drive sun gear, respectively. A friction clutch driveably connects the transmission output and a drive shaft.
Each of these transmissions produces reverse drive and low speed forward drive by alternately depressing pedals that cause engagement of a corresponding brake band. Direct drive results when these pedals are released. The axial position of each brake band is fixed so that the band continually surrounds the corresponding brake drum; its position is not altered by any other action including manipulation of a gear selector lever by the vehicle operator.